Add a tea.Sequentially command

Signed-off-by: Carlos Alexandro Becker <caarlos0@gmail.com>

commands.go

@@ -51,3 +51,27 @@ func Tick(d time.Duration, fn func(time.Time) Msg) Cmd {
 		return fn(<-t.C)
 	}
 }
+
+// Sequentially produces a command that sequentially executes the given
+// commands.
+// The Msg returned is the first non-nil message returned by a Cmd.
+//
+//   func saveStateCmd() Msg {
+//   	if err := save(); err != nil {
+//    		return errMsg{err}
+//    	}
+//   	return nil
+//   }
+//
+//   cmd := Sequentially(saveStateCmd, Quit)
+//
+func Sequentially(cmds ...Cmd) Cmd {
+	return func() Msg {
+		for _, cmd := range cmds {
+			if msg := cmd(); msg != nil {
+				return msg
+			}
+		}
+		return nil
+	}
+}

commands_test.go

@@ -0,0 +1,56 @@
+package tea
+
+import (
+	"fmt"
+	"testing"
+)
+
+func TestSequentially(t *testing.T) {
+	var expectedErrMsg = fmt.Errorf("some err")
+	var expectedStrMsg = "some msg"
+
+	var nilReturnCmd = func() Msg {
+		return nil
+	}
+
+	tests := []struct {
+		name     string
+		cmds     []Cmd
+		expected Msg
+	}{
+		{
+			name:     "all nil",
+			cmds:     []Cmd{nilReturnCmd, nilReturnCmd},
+			expected: nil,
+		},
+		{
+			name: "one error",
+			cmds: []Cmd{
+				nilReturnCmd,
+				func() Msg {
+					return expectedErrMsg
+				},
+				nilReturnCmd,
+			},
+			expected: expectedErrMsg,
+		},
+		{
+			name: "some msg",
+			cmds: []Cmd{
+				nilReturnCmd,
+				func() Msg {
+					return expectedStrMsg
+				},
+				nilReturnCmd,
+			},
+			expected: expectedStrMsg,
+		},
+	}
+	for _, test := range tests {
+		t.Run(test.name, func(t *testing.T) {
+			if msg := Sequentially(test.cmds...)(); msg != test.expected {
+				t.Fatalf("expected a msg %v but got %v", test.expected, msg)
+			}
+		})
+	}
+}